Electronic circuits which receive video signals frequently have a need to ensure a synchronization between the incoming signals and the rate at which the system operates. This phenomenon is usually referred to as time base correction and is often required particularly when digital signal processing is performed on video signals because the digital video information to be processed must be in sync with a standard format to be able to process it. Time base correctors can synchronize to non-synchronous video sources, store a field of video information for electronic shuttering (that is taking a snap-shot of the video information stored, similar to a camera versus a movie projector), quantize and digitize for recursive filtering (summing several looks at a scene to eliminate background noise so that the real picture is reinforced with each view and the sporadic/electronic background noise is thereby attenuated), and perform other types of digital processing.
To date, no real time solid state TV field processor on a cathode ray tube is known to be available which is small in size or synchronized such that it handles a frame in like manner (a frame is two fields placed in such a manner to give the appearance of 525 lines, rastored twice by interlacing the beam). One-line time base correctors and full scan converters are available; however, such devices don't meet the small scale, solid state compactness and reliability required. The one line time base correctors and full scan converters compromise a CRT display and a video camera looking at the display in real time and tend to be very expensive. They also are of low reliability when attempted to be used in highly demanding military applications.
Typical of the variety of approaches is the apparatus of U.S. Pat. No. 3,573,358 which has a time base correction to an electron beam to correct alignment error of a film. It gets its correlation signals from phase and quadrature signals and not from a digitized memory. The synchronizing arrangement of U.S. Pat. No. 3,887,941 uses a process of phase-locked loops and counters to regenerate the sync of a video tape recorder and appears not be be capable of correcting two different time bases. The signal processing of U.S. Pat. No. 4.074,307 employs CCD devices for memory and correct one to two lines at a time. The CCD's purpose appears to be incapable of providing for full field or frame time base correction. Another clock generator disclosed in U.S. Pat. No. 4,110,785 allows for the processing of only one or two lines at a time and, while a noteworthy advance, field or frame correction is not possible in this device. The time base error correcting apparatus of U.S. Pat. No. 4,287,529 is similar in application yet its design allows for the correction of one or two lines at a time and may be lacking of a full field or frame of memory for vertical correction so that timing of frames or fields due to vertical instabilities is beyond its capabilities. The corrector system of U.S. Pat. No. 4,297,728 employs CCD's for one line correction. Full field or framed time base errors are not corrected largely because of the CCD's.
Thus, there is a continuing need in the state of the art for a solid state time base corrector for synchronizing an external video field with a local time base crystal that generates its own time frame reference for a one full scan of a CRT display.